Photovoltaic cell having a coupled expanded metal article

ABSTRACT

In embodiments, a photovoltaic cell has an expanded metal article configured as a mesh, a semiconductor material, and a front metallic article. The expanded metal article has a plurality of first segments intersecting a plurality of second segments thereby forming a plurality of openings, and has a plurality of cuts in the mesh. The expanded metal article is electrically coupled to a back surface of the semiconductor material. The front metallic article has a plurality of electroformed elements interconnected to form a unitary, free-standing piece comprising a continuous grid. The continuous grid of the front metallic article is electrically coupled to a front surface of the semiconductor material. The plurality of cuts of the expanded metal article is arranged on the photovoltaic cell to relieve stresses induced by the front metallic article on the front surface of the semiconductor material.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/238,525, filed on Jan. 3, 2019 and entitled “Photovoltaic Cell Havinga Coupled Expanded Metal Article”; which is a continuation-in-part ofU.S. patent application Ser. No. 15/382,304, filed on Dec. 16, 2016,entitled “Photovoltaic Cell Having a Coupled Expanded Metal Article” andissued as U.S. Pat. No. 10,181,542; which is a continuation-in-part ofInternational PCT Application No. PCT/US15/32622, filed on May 27, 2015and entitled “Photovoltaic Cell Having a Coupled Expanded MetalArticle”; which claims priority to U.S. Provisional Patent ApplicationNo. 62/014,950, filed on Jun. 20, 2014 and entitled “Photovoltaic CellHaving a Coupled Expanded Metal Article”; all of which are herebyincorporated by reference for all purposes.

BACKGROUND

A solar cell is a device that converts photons into electrical energy.The electrical energy produced by the cell is collected throughelectrical contacts coupled to the semiconductor material, and is routedthrough interconnections with other photovoltaic cells in a module. The“standard cell” model of a solar cell has a semiconductor material, usedto absorb the incoming solar energy and convert it to electrical energy,placed below an anti-reflective coating (ARC) layer, and above a metalbacksheet. Electrical contact is typically made to the semiconductorsurface with fire-through paste, which is metal paste that is heatedsuch that the paste diffuses through the ARC layer and contacts thesurface of the cell. The paste is generally patterned into a set offingers and bus bars which will then be soldered with ribbon to othercells to create a module. Another type of solar cell has a semiconductormaterial sandwiched between transparent conductive oxide layers (TCO's),which are then coated with a final layer of conductive paste that isalso configured in a finger/bus bar pattern.

In both these types of cells, the metal paste, which is typicallysilver, works to enable current flow in the horizontal direction(parallel to the cell surface), allowing connections between the solarcells to be made towards the creation of a module. Solar cellmetallization is most commonly done by screen printing a silver pasteonto the cell, curing the paste, and then soldering ribbon across thescreen printed bus bars. However, silver is expensive relative to othercomponents of a solar cell, and can contribute a high percentage of theoverall cost.

To reduce silver cost, alternate methods for metallizing solar cells areknown in the art. For example, attempts have been made to replace silverwith copper, by plating copper directly onto the solar cell. However, adrawback of copper plating is contamination of the cell with copper,which impacts reliability. Plating throughput and yield can also beissues when directly plating onto the cell due to the many stepsrequired for plating, such as depositing seed layers, applying masks,and etching or laser scribing away plated areas to form the desiredpatterns. Other methods for forming electrical conduits on solar cellsinclude utilizing arrangements of parallel wires or polymeric sheetsencasing electrically conductive wires, and laying them onto a cell.However, the use of wire grids presents issues such as undesirablemanufacturing costs and high series resistance.

Furthermore, in Babayan et al., U.S. Pat. Nos. 8,569,096 and 8,936,709,which are owned by the assignee of the present application and areincorporated in their entirety by reference herein, electrical conduitsfor semiconductors such as photovoltaic cells are fabricated as anelectroformed free-standing metallic article which are subsequentlyattached to a semiconductor material. The metallic articles are producedseparately from a solar cell and can include multiple elements such asfingers and bus bars that can be transferred stably as a unitary pieceand easily aligned to a semiconductor device. The elements of themetallic article are formed integrally with each other in theelectroforming process. However, the metallic article is manufactured inan electroforming mandrel, which, while generating a patterned metallayer that is tailored for a solar cell or other semiconductor device,requires additional equipment and cost.

Therefore, there is a need in the industry for low cost methods forattaching electrically conductive elements to the surface of asemiconductor material to thereby form a photovoltaic cell.

SUMMARY

In some embodiments, a photovoltaic cell includes an expanded metalarticle, a semiconductor material and a front metallic article. Theexpanded metal article is configured as a mesh, the mesh having aplurality of first segments intersecting a plurality of second segmentsthereby forming a plurality of openings. The expanded metal article hasa plurality of cuts in the mesh. The semiconductor material has a frontsurface that serves as a light-incident surface of the photovoltaic celland a back surface opposite the front surface. The expanded metalarticle is electrically coupled to the back surface of the semiconductormaterial. The front metallic article has a plurality of electroformedelements interconnected to form a unitary, free-standing piececomprising a continuous grid. The continuous grid of the front metallicarticle is electrically coupled to the front surface of thesemiconductor material. The plurality of cuts of the expanded metalarticle is arranged on the photovoltaic cell to relieve stresses inducedby the front metallic article on the front surface of the semiconductormaterial.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the presentinvention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Each of the aspects and embodiments described herein can be used aloneor in combination with one another. The aspects and embodiments will nowbe described with reference to the attached drawings.

FIG. 1 shows an embodiment of an expanded metal article used to form aphotovoltaic cell, in accordance with some embodiments.

FIG. 2 shows a top view of a formed photovoltaic cell, in accordancewith some embodiments.

FIG. 3 shows a bottom view of an embodiment of a formed photovoltaiccell, in accordance with some embodiments.

FIG. 4A is a plan view of an expanded metal article with cuts toaccommodate thermal expansion, in accordance with some embodiments.

FIG. 4B is a detailed view of FIG. 4A.

FIG. 4C is a side view of a photovoltaic assembly, in accordance withsome embodiments.

FIG. 4D is a back view of the photovoltaic assembly of FIG. 4C.

FIG. 5 is a plan view of an example photovoltaic cell onto which anexpanded metal article with cuts has been mounted.

FIG. 6 is a perspective view of a metal cutting assembly, in accordancewith some embodiments.

FIG. 7 shows the metal cutting assembly of FIG. 6, with an expandedmetal material inserted.

FIG. 8 shows the metal cutting assembly of FIG. 7, with the expandedmetal material held between a holding plate and a receiving plate of theassembly.

FIG. 9 shows the metal cutting assembly of FIG. 7 after cuts have beencreated in the expanded metal material.

FIG. 10 is a flowchart of methods for forming a photovoltaic cell, inaccordance with embodiments of the present disclosure.

FIG. 11 is a flowchart of further methods for forming a photovoltaiccell, in accordance with embodiments of the present disclosure.

It should be understood that the above-referenced drawings are notnecessarily to scale, presenting a somewhat simplified representation ofvarious features illustrative of the basic principles of the disclosure.The specific design features of the present disclosure, including, forexample, specific dimensions, orientations, locations, and shapes, willbe determined in part by the particular intended application and useenvironment.

DETAILED DESCRIPTION

The present disclosure relates to photovoltaic cells comprising attachedexpanded metal articles. The expanded metal articles are configured as amesh and have cuts in the mesh, where the expanded metal articles arearranged on photovoltaic cells such that the cuts relieve thermal andmechanical stresses of the assembled photovoltaic cell.

According to some embodiments, the method comprises the step ofproviding an expanded metal article, providing a semiconductor material,and electrically coupling them. The term “expanded metal article” refersto metallic articles prepared by a known process in which metal in theform of a sheet or plate is simultaneously slit and stretched (i.e.,expanded) in defined patterns to produce a metallic article having acontinuous mesh or grid-like structure. While similar grid patterns canalso be formed in metallic sheets by stamping operations, these methodsproduce a significant amount of waste material. By comparison, theexpanded metal process disclosed herein essentially produces a metallicarticle having specifically designed openings or holes without removingany material to produce them. The resulting expanded metal can be takenup in rolls and subsequently cut into specific sized free-standingpieces for various applications.

The expanded metal article used in the present methods can comprise anymetal, for instance a conductive metal, that can be formed into a gridusing the expanded metal process. For example, the expanded metalarticle may comprise nickel, copper, aluminum, silver, palladium,platinum, titanium, or galvanized or stainless steel. Alloys of thesemetals can also be used. In some embodiments, the expanded metal articlecomprises copper, and is a copper grid.

The expanded metal article comprises a plurality of first segmentsintersecting a plurality of second segments forming an opening, and theshape of the opening is not particularly limited. For example, theopenings in the article can be diamond shaped, square, hexagonal, ovoid(having a shape similar to an egg or oval), or circular. These shapesmay also be elongated, depending on the directionality of the process bywhich the openings are formed and expanded. Also, irregular shapes arealso possible, depending, for example, on how the slit in the startingmetallic sheet is created and expanded. The size of the opening and thesize of the first and second elements can also vary, depending, forexample, on which side of the semiconductor material the expanded metalarticle is to be electrically coupled, described in more detail below.For example, the opening can have a dimension (such as a length or awidth) of from about 2 mm to about 20 mm. As a specific example, theexpanded metal article can comprise diamond shaped openings having awidth of from about 2 mm to about 10 mm, such as about 3 mm to about 7mm, and a length of from about 5 mm to about 20 mm, such as about 10 mmto about 15 mm. Furthermore, the first and second segments can have awidth of from about 0.5 mm to about 10 mm, including from about 1 mm toabout 5 mm. Thinner segments can also be used, as long as the expandedmetallic article remains as a continuous grid during handling.

The thickness of the expanded metal article can also vary depending on,for example, cost, handling characteristics, the thickness of themetallic sheet from which it was made, as well as the desired electricalcurrent carrying needs of the resulting photovoltaic cell. For example,the expanded metal article can have a thickness of from about 25 micronsto about 300 microns, including from about 50 microns to about 200microns and from about 75 microns to about 150 microns. Thinner expandedmetal articles can be used for highly conductive metals withoutsacrificing photovoltaic performance, while relatively thicker articlescan be used for metals with poorer mechanical strength but lower cost(including processing costs).

In some embodiments, the expanded metal article further comprises aplurality of soldering points which are configured to enable the metalarticle to be electrically coupled to a semiconductor material to form aphotovoltaic cell. The soldering points can be located at variouspositions on either the top or bottom surface of the expanded metalarticle and can comprise any soldering material known in the art. Forexample, the soldering points may be solder pads having, for example,square, rectangular, or round shapes, and these pads can be positionedon the intersecting first and second elements or at the intersection ofthese elements. Alternatively, or in addition, the soldering pointscomprise areas of higher amounts of solder compared to the rest of thesurface of the expanded metal article. For example, the surface of anexpanded copper metal article to be coupled to the semiconductormaterial may be coated by a layer of solder having a thickness of fromabout 1 to about 10 microns, such as from 2 to about 5 microns, whichcan be used, for example, to help prevent copper electromigration, andfurther may include a plurality of locations comprising solder having athickness of from about 15 to about 30 microns, such as from about 20 toabout 25 microns. In an example embodiment, the expanded metal articlemay be coated with an initial layer of solder coating, such as byelectroplating. The solder coating may have a thickness of, for example,from about 1 to about 10 microns, or from 2 to about 5 microns.Additional solder may then be applied onto the solder coating to preparefor soldering which electrically couples the expanded metal article tothe semiconductor material. The additionally applied solder may besupplied from, for example, a solder ribbon or a solder paste that canbe applied during any point in the assembly process. For example, theapplied solder can be solder pads that are formed on the expanded metalarticle prior to placing the metal article onto the semiconductormaterial. Alternatively, the solder pads created by the applied soldercan be added during or after the placement of the expanded metal articleonto the semiconductor material. For any of these soldering embodiments,flux may also be applied during the soldering process according tostandard techniques.

A specific example of an embodiment of the expanded metal article usedin the present methods is shown in FIG. 1. It should be apparent tothose skilled in the art that the figures presented are merelyillustrative in nature and not limiting, being presented by way ofexample only. Numerous modifications and other embodiments are withinthe scope of one of ordinary skill in the art, given the benefit of thepresent disclosure, and are contemplated as falling within the scope ofthe present disclosure. In addition, those skilled in the art shouldappreciate that the specific configurations are exemplary and thatactual configurations will depend on the specific system. Those skilledin the art will also be able to recognize and identify equivalents tothe specific elements shown, using no more than routine experimentation.

As shown in FIG. 1, expanded metal article 10 comprises a plurality offirst elements 11 intersecting a plurality of second elements 12,forming a continuous grid or mesh structure having a plurality ofopenings 13, which, in this example, are diamond shaped. The openings 13can be made by making slits in a piece of sheet metal and stretching thesheet metal so that the sheet metal is expanded at the slits. Forexample, in FIG. 1 if slits are made in the vertical direction(y-direction) then the sheet metal is stretched (i.e., expanded) in thehorizontal direction (x-direction) as indicated by arrow 15 representingthe expansion direction. In FIG. 1, the long way of the openings 13 isin the vertical direction, and the short way of the openings 13 is inthe horizontal direction which is also the expansion direction in thisembodiment. The long way of the openings 13 is the length of the longdiamond diagonal, while the short way of the openings 13 is the lengthof the short diamond diagonal. Expanded metal article 10 furthercomprises a plurality of solder pads 14, which, as shown, are positionedaround the surface of expanded metal article 10 at intersection pointson the periphery of the surface as well as in interior locations.

As described above, methods of the present disclosure compriseelectrically coupling or attaching the expanded metal article to asemiconductor material, such as amorphous silicon, crystalline silicon(including multicrystalline and monocrystalline silicon), or any othersemiconductor material suitable for use in a photovoltaic cell. Thesemiconductor material can vary in size and shape and can comprise, forexample, a square multicrystalline silicon cell or a monocrystallinesilicon cell having rounded corners, sometimes referred to as apseudosquare shape. Others will be known in the art.

The semiconductor material has a top (i.e., front) surface, which is thelight incident surface of the photovoltaic cell to be formed, and abottom (i.e., back) surface, which is the opposite side of the cell notexposed to light, and the expanded metal article can be electricallycoupled to either surface. While the coupling can occur anywhere on thesurfaces of either the expanded metal article or the semiconductormaterial, in some embodiments the metallic article and semiconductormaterial coincide, with the expanded metal article substantiallyspanning a surface, such as the top or bottom surface, of thesemiconductor material. However, it is also possible for the expandedmetal article to extend beyond the semiconductor surface, therebyforming an interconnection element that can be used to connect multiplephotovoltaic cells together to form a module. At least one surface ofthe semiconductor material comprises a plurality of points of contactfor the expanded metal article. In some embodiments, a majority of thesoldering points on the surface of the expanded metal article areelectrically coupled and, as such, are in electrical contact with, theplurality of points of contact on the semiconductor material. That is,the majority of the plurality of solder pads on the surface of theexpanded metal article are electrically coupled at a plurality ofsoldering locations with the plurality of silver pads on the surface ofthe semiconductor material.

The points of contact on the surface of the semiconductor material willdepend, for example, on which surface the metallic article is coupled.In one embodiment, the top surface of the semiconductor materialcomprises a plurality of silver segments, and the expanded metal articleis coupled to these segments. The plurality of silver segments can be,for example, a linear array of parallel silver fingers traversing thetop surface of the semiconductor material from one edge to an oppositeedge. Such an arrangement is common and well known in photovoltaiccells. Alternatively, the silver segments can be linear segments ofsilver arranged linearly across the semiconductor surface, forming, forexample, broken parallel silver lines or fingers traversing from oneedge of the surface to an opposite edge. Other arrangements are alsopossible and will be known to one skilled in the art.

For this embodiment, since the top surface will be exposed to light, itis important that the expanded metal article have opening sizes andsegment widths that minimize shading to the semiconductor surface andthus has a high percent open area (which is the percentage of thesemiconductor material not shaded by the metallic article). Theresulting photovoltaic cell of this embodiment has a percent open areagreater than about 90%, such as greater than about 93%, or such asgreater than about 95%.

In another embodiment of the present methods, the expanded metal articleis electrically coupled to the bottom (back) surface of thesemiconductor material, which comprises a plurality of silver pads asthe points of contact. The silver pads can be any shape, such as, forexample, square, rectangular, or round, and may be the same or differentin size and/or shape than the solder pads on the surface of the expandedmetal article. The silver pads can be positioned anywhere around thebottom surface of the semiconductor material, including in an evenlydistributed regular array. Additional silver pads may be positionedaround the edges of the semiconductor material, thereby ensuring asecure contact.

For this embodiment, since the bottom surface of the semiconductormaterial will not be exposed to light, constraints relating to shadingcan be relaxed compared to the requirements of the top surface. Thus,opening sizes and segment widths of the expanded metal article can belarger for this embodiment and the percent open area can be less. Forexample, the resulting photovoltaic cell of this embodiment has apercent open area greater than about 80%, such as greater than about85%, or such as greater than about 90%.

Specific examples of the resulting photovoltaic cells produced in themethod of the present disclosure are shown in FIG. 2 and FIG. 3. Thus,in FIG. 2, expanded metal article 20, comprising a plurality of solderpads 24, is shown electrically coupled to the top surface ofsemiconductor material 25, which comprises a plurality of silversegments 26. Also, in FIG. 3, expanded metal article 30, comprising aplurality of solder pads 34, is shown electrically coupled to the bottomsurface of semiconductor material 35, comprising a plurality of squaresilver pads 37. As can be seen in FIGS. 2 and 3, a majority of solderpads 24 and 34 are in electrical contact with silver segments 26 orsilver pads 37, respectively, where the locations of electrical contactare soldering locations at which the expanded metal article 20 or 30 areelectrically coupled to the semiconductor material 25 or 35.

As discussed above, one or both surfaces of the semiconductor materialmay be electrically coupled with the expanded metal article. If only onesurface is used, the other surface can be coupled using any known methodto complete the circuit in the photovoltaic cell. For example, in thepresent methods, a free-standing metallic article that differs from theexpanded metal article, can be electrically coupled to the availablesemiconductor surface to form the photovoltaic cell. In particular, ametallic article comprising a plurality of electroformed elementsinterconnected to form a unitary, free-standing piece comprisinggridlines can be used, such as those described in U.S. Pat. Nos.8,569,096 and 8,936,709. In some embodiments, the electroformed metallicarticle can be used as a front metallic article on the front,light-incident surface of a photovoltaic cell, while the expanded metalarticle may be used on the back surface. The electroformed elements ofthe front metallic article may also include a cell-to-cell interconnectthat is integral with the continuous grid and is coupled to aneighboring back surface of a neighboring photovoltaic cell, asdescribed in U.S. Pat. No. 8,936,709 and U.S. patent application Ser.Nos. 15/192,576 and 16/030,766 which are owned by the assignee of thepresent disclosure and are hereby incorporated by reference.

FIGS. 4A-4B illustrate further embodiments in which the expanded metalarticles of the present disclosure include a plurality of cuts toaccommodate a difference in coefficient of thermal expansion between theexpanded metal article and the semiconductor material. FIG. 4A is a fullview of an expanded metal article 40, while FIG. 4B is a detailed view.The expanded metal article 40 has a plurality of intersecting firstsegments 41 and a plurality of second segments 42 that form a pluralityof openings 43 as described above for previous embodiments. The metalarticle 40 also has a plurality of cuts 44 that form discontinuities inthe grid, where each cut 44 extends across at least one of the firstsegments 41, one of the second segments 42, and/or an intersection ofone of the first segments 41 and one of the second segments 42. In themetal article 40 of FIGS. 4A-4B, each cut 44 is depicted as extendingacross two intersections of the first segments 41 and second segments42; however, other lengths of cuts 44 are possible.

The plurality of cuts 44 allow portions of the metal article 40 tofreely expand and contract, and provide mechanical flexion within themetal article 40, thus relieving thermal stresses induced during bondingof the metal article to the semiconductor wafer. In the embodiment ofFIGS. 4A-4B, the cuts 44 are arranged as an orthogonal array, withdimensions of the array chosen to accommodate a difference incoefficient of thermal expansion between the expanded metal article andthe semiconductor material. For instance, array dimensions may include alateral spacing 46 of about 10 to 15 mm and a lengthwise spacing 47(from the end of one cut to the start of the next cut) of about 3-7 mmfor a 156 mm by 156 mm photovoltaic cell. Instead of an orthogonal arraywhere the cuts 44 are aligned horizontally and vertically with eachother, the array may be a staggered array in which the cuts 44 arediagonally aligned with each other. Other array layouts are alsopossible, which could include having arrays of cuts 44 only in certainregions of the metal article 40, such as where higher stresses areexpected. Furthermore, the cuts 44 need not be arranged in an array,such as being randomly placed across the metal article 40. Arraydimensions may be uniform throughout the array, or may be different incertain regions such as near the perimeter of the metal article 40.

The array dimensions also include the dimensions of the cuts 44, wherefor a 156 mm by 156 mm photovoltaic cell the cuts 44 may have a length48 ranging from, for example, 3 to 7 mm, and a width 49 ranging from,for example, 0.1 to 1 mm. Note that the endpoints of the lengths 47 and48 are denoted as being from the center of each opening 43 in thisembodiment, although other conventions may be utilized as desired forspecifying the dimensions of the cuts 44. The specific geometricalarrangement of the plurality of cuts 44 and dimensions of the array ofcuts are chosen based on the specific materials being used for thephotovoltaic cell and the temperature ranges to which the materials areanticipated to be exposed. Furthermore, the arrangement of the pluralityof cuts described above may also be arranged to relieve thermal stressesinduced by a front metallic article on a front surface of thesemiconductor material. For example, expansion or contraction of thefront metallic article may impart mechanical and/or thermal stresses onthe semiconductor material, which may then cause mechanical and/orthermal stresses on the expanded metal article on the back surface ofthe semiconductor material.

In addition to the thermal expansion stresses, the semiconductormaterial may also experience mechanical stresses imposed by aninterconnect and/or a metallic article that serves as an electricalconduit attached to the front (i.e., top) surface of the semiconductor.FIG. 4C shows a simplified side view of an assembled photovoltaic cell400 (not to scale) which includes a semiconductor material 410 having afront surface 412 and a back surface 414, where the front surface 412 isthe light-incident surface of the cell 400. A front metallic article420—which may be, for example, electroformed—is coupled to the frontsurface 412 and has a continuous grid 422 that is integrally formed witha cell-to-cell interconnect 424. An expanded metal article 430, such asexpanded metal article 40 of FIG. 4A, is coupled to the back surface414. In a photovoltaic module containing the photovoltaic cell 400, thecell-to-cell interconnect 424 is coupled to a back surface of anadjacent photovoltaic cell 401. The coupling of cells 400 and 401together in this manner may create mechanical stresses causing thesemiconductor wafer 410 to warp or bow as indicated by arrow 450. Thespecific arrangement of cuts in the expanded metal article 430 on theback (i.e., bottom) surface 414 of the semiconductor material 410 can bechosen to balance out these mechanical stresses, thereby enabling thesemiconductor to remain flat. That is, in some embodiments the pluralityof cuts is arranged to relieve mechanical stresses induced by the frontmetallic article 422 on the top surface 412.

FIG. 4D shows an example embodiment of orienting the cuts in the mesh ofthe expanded metal article relative to the other components to relievemechanical stresses. In this back view, the expanded metal article 430is seen, mounted on semiconductor material 410. The cell-to-cellinterconnect 424 is seen spanning across and extending beyond a firstedge 416 of the front surface 412 of the semiconductor material 410. InFIG. 4D, a plurality of cuts 435 are in the mesh of expanded metalarticle 430, where the cuts 435 have a length “L” extending in a firstdirection 438 that is parallel to the first edge 416. This orientationof the cuts 435 enables the expanded metal article 430 to accommodatethe mechanical stresses resulting from bowing of the photovoltaic cellin the direction indicated by arrow 450 of FIG. 4C. Arrow 450 representsa bowing of the photovoltaic cell 400 about an axis that is parallel tothe first edge 416, which is also approximately parallel to thedirection 438 of the cuts 435. In some embodiments, at least one, suchas a majority or all of the cuts 435 are oriented to accommodate themechanical stresses of the bowing or warping of the photovoltaic cell400 that are caused by the cell-to-cell interconnect 424 being coupledto neighboring photovoltaic cell 401. In other embodiments, some cutsmay be oriented to accommodate the bowing while other cuts may beoriented and/or arranged (e.g., positioned and/or dimensioned) for othermechanical stresses and/or thermal stresses. For example, some of thecuts 435 may be positioned between the solder pads 418 (on semiconductormaterial 410) when the expanded metal article 430 is coupled to thesemiconductor wafer 410, to allow for expansion and contraction of theexpanded metal article 430 between the fixed solder points 418.

In various embodiments, the number, density, orientation, and locationof cuts can vary depending on the location and magnitude of stress to becounter-balanced. For example, the overall number, density, and/or sizeof the cuts can be increased for instances in which higher stresses areanticipated, such as in aerospace applications due to the extremeenvironmental conditions. The configuration of the cuts may also dependon the thickness of the semiconductor material being used, as thickersemiconductor materials may experience less bowing or warping and thusmay utilize smaller cuts in the expanded metal article than photovoltaiccells that use thinner semiconductor materials. In another example, thedirection (i.e., orientation) of the cuts can be arranged according tothe direction of the stresses that are to be relieved. Furthermore, asthe distribution of stresses imposed on the semiconductor is likely tobe spatially asymmetric with respect to the location on thesemiconductor, the number, size, orientation, and density of cuts can betailored to balance out these regional stresses. For example, higherstress can be incurred on the corners and edges of the semiconductor dueto geometrical effects. To counter-balance these stresses, a greaterdensity of cuts or larger sized cuts may be placed at the corners andedges of the expanded metal article to give additional stress relief.

In some embodiments, the expanded metal article has an expansiondirection in which the plurality of openings was formed (see arrow 15 ofFIG. 1), and at least one cut of the plurality of cuts has a lengthextending in a first direction that is oriented in the expansiondirection. In FIG. 4D, for example, the cuts 435 have a length that isoriented across the short way of the openings in the mesh (x-directionin FIG. 4D), which is the expansion direction of the expanded metalarticle in this embodiment. That is, the plurality of cuts 435 has alength extending in a first direction that is oriented in the expansiondirection, and the first direction is oriented in a short way of theplurality of openings (horizontal, x-direction in FIG. 4D). By cuttingacross the slits that were made to expand the metal sheet, mechanicalstresses from the metal trying to rebound back into its originalunstretched state can be relieved. Relieving at least some of themechanical stress that is innate in the expanded metal article due toits forming process also helps prevent the expanded metal articleimparting stresses to the semiconductor material (e.g., causing thesemiconductor material to bow) when the expanded metal article iscoupled to the photovoltaic cell. Additionally, innate stresses in theexpanded metal article from the forming process can be oriented in adifferent direction from the bowing that is imparted by coupling thecell-to-cell interconnect to a neighboring cell. For example, theexpansion direction of the expanded metal article can be oriented in thesame direction as the edge along which the cell-to-cell interconnectspans. In this manner, potential warping caused by innate mechanicalstresses of the expanded metal article are approximately perpendicularand may reduce or cancel out potential mechanical warping caused by theinterconnection between photovoltaic cells.

FIG. 5 shows a back view of another photovoltaic cell 50 onto which theexpanded metal article 40 with cuts 44 has been mounted. A cell-to-cellinterconnect of a front metallic article is not included in this view,for clarity. FIG. 5 depicts soldering locations 52, which are linearpaths across a length of the photovoltaic cell 50 in this embodiment. Atleast some of the plurality of cuts 44 are between neighboring solderinglocations; that is, being bordered by the nearest two solderinglocations 52. For example, in FIG. 5 the cuts 44 are perpendicular tothe linear soldering locations 52 and extend across a majority of thedistance between the soldering lines. As an example embodiment, for aspacing of about 15 mm between the soldering lines (locations) 52, thecuts may extend approximately 10 to 13 mm across that distance. In otherembodiments, the cuts 44 span various portions of the distances betweensoldering locations, and may be at any orientation with respect to thesoldering locations 52, such as parallel, perpendicular, or any anglebetween. In some embodiments, the cuts 44 do not necessarily need to allbe between soldering points (soldering locations 52). However, the cuts44 that are between soldering locations 52 provide stress relief byallowing the expanded metal article, solder, and the semiconductor waferto expand and contract relative to each other, compared to the fixedpoints where the metal article 40 is joined to the photovoltaic cell 50.

FIG. 6 is a perspective view of an example metal cutting assembly 60that may be used to create cuts within the expanded metal article. Metalcutting assembly 60 includes a cutting tool 62, a holding plate 64, anda receiving plate 66, where the holding plate 64 is stacked between thecutting tool 62 and the receiving plate 66. Cutting tool 62 has aplurality of cutting elements 63 facing holding plate 64, where thecutting elements 63 serve as knife blades that pierce through theexpanded metal article to form cuts (e.g., cuts 44 of FIG. 4). Thecutting elements 63 may be made of, for example stainless steel. Inoperation, the cutting tool 62, holding plate 64, and receiving plate 66are pressed together, such as by manual or automatic actuation.

FIGS. 7-9 show stages of forming the cuts in the expanded metal articleusing the metal cutting assembly 60. An expanded metal article 70 isprovided, such as being supplied from a roll of expanded mesh material,or alternatively supplied as an individual piece. Next, as shown in FIG.7, an expanded metal article 70 is inserted between the holding plate 64and the receiving plate 66. In FIG. 8, the holding plate 64 is loweredto hold the expanded metal article 70 between the holding plate 64 andthe receiving plate 66. The cutting tool 62 is then lowered as indicatedby arrows 80, such that the cutting elements 63 penetrate through theholding plate 64 and the receiving plate 66 and form a plurality of cuts74 in the expanded metal article 70, as shown in FIG. 9. In someembodiments, the holding plate 64 and receiving plate 66 may be made ofa metal such as stainless steel or aluminum, having pre-formed apertures65 through which the cutting elements 63 can extend. In otherembodiments, the holding plate 64 and receiving plate 66 may be made ofa material that the cutting elements can pierce, without requiringpre-formed apertures. The cutting tool 62 is then raised while theholding plate 64 remains in place, with the metal article 70 sandwichedbetween the holding plate 64 and receiving plate 66, to assist inseparating the cutting elements 63 from the expanded metal article 70and to prevent the expanded metal article 70 from deforming as thecutting elements 63 are removed.

In some embodiments, the process can also involve a sizing tool—as partof or as a separate component from the metal cutting assembly 60—to trimthe outer perimeter of the expanded metal article 70 to the necessarysize and shape for a photovoltaic cell. For example, the length and/orwidth of the overall expanded metal article can be cut to approximately156 mm for a 156 mm² photovoltaic cell. If the expanded mesh materialfor the metal article is supplied from a roll, the roll may bepre-fabricated to 156 mm such that only one end of the mesh materialneeds to be cut to length. Additionally, for a monocrystalline cell thesizing tool may be configured to create the corners 75 of thepseudosquare shape while the expanded metal article 70 is held in themetal cutting assembly 60.

FIG. 10 is a flowchart 100 of methods for forming a photovoltaic cell inaccordance with embodiments of the present disclosure. In step 110, anexpanded metal article is provided, having a plurality of first segmentsintersecting a plurality of second segments forming a plurality ofopenings. In some embodiments, the expanded metal article has a surfacecomprising a plurality of solder pads.

In some embodiments, the expanded metal article has a plurality of cuts,such as created by a metal cutting assembly provided in step 120. Eachcut in the plurality of cuts creates a discontinuity in the expandedmetal article. That is, the cuts are breaks in the first segments and/orsecond segments that allow strain within the metal article or within thephotovoltaic cell assembly to be relieved. The metal cutting assemblyincludes a cutting tool, a receiving plate, and a holding plate. Theholding plate is stacked between the cutting tool and the receivingplate, and the cutting tool comprises a plurality of cutting elementsfacing the holding plate. After the expanded metal article is providedin step 110, the expanded metal article is inserted between the holdingplate and the receiving plate. The cutting tool is moved toward theholding plate and the receiving plate, as described in FIGS. 6-9, suchthat the plurality of cutting elements penetrates through the holdingplate and the receiving plate and forms a plurality of cuts in theexpanded metal article.

In step 130, a semiconductor material is provided, where thesemiconductor material has a top surface that serves as a light-incidentsurface of the photovoltaic cell, and a bottom surface opposite the topsurface. In step 140, the expanded metal article is electrically coupledwith the semiconductor material at a plurality of soldering locations.For example, the expanded metal article is electrically coupled to aplurality of silver pads on the bottom surface of the semiconductormaterial. In embodiments in which the expanded metal article is providedwith solder pads, a majority of the plurality of solder pads on thesurface of the expanded metal article is electrically coupled with theplurality of silver pads on the bottom surface of the semiconductormaterial at a plurality of soldering locations. In some embodiments, theexpanded metal article has a solder coating, and the electrical couplingof step 140 involves soldering the expanded metal article to theplurality of silver pads with an applied solder that is placed onto thesolder coating.

In embodiments in which the expanded metal article has cuts for thermalor mechanical relief, at least one cut in the plurality of cuts iswithin a region between neighboring soldering locations of the pluralityof soldering locations. The plurality of cuts can be arranged as anarray having array dimensions configured to accommodate a difference incoefficient of thermal expansion between the expanded metal article andthe semiconductor material.

FIG. 11 is a flowchart 101 of methods for forming a photovoltaic cell inaccordance with embodiments of the present disclosure, where a pluralityof cuts in an expanded metal article are arranged to relieve stresses.In some embodiments, the methods optionally include forming theplurality of cuts in steps 111-113, prior to step 121. Step 111 involvesproviding a metal cutting assembly, the metal cutting assemblycomprising a cutting tool, a receiving plate, and a holding plate. Theholding plate is stacked between the cutting tool and the receivingplate, where the cutting tool comprises a plurality of cutting elementsfacing the holding plate. Step 112 involves inserting an expanded metalmesh (sheet metal having openings formed into a mesh configuration, butno cuts in the mesh) between the holding plate and the receiving plate.Step 113 involves moving the cutting tool toward the holding plate andthe receiving plate such that the plurality of cutting elementspenetrates through the holding plate, the expanded metal mesh and thereceiving plate, resulting in the plurality of cuts being formed in theexpanded metal article.

Step 121 involves providing the expanded metal article configured as amesh. The mesh has a plurality of first segments intersecting aplurality of second segments thereby forming a plurality of openings.The expanded metal article has a plurality of cuts in the mesh, and theexpanded metal article has a surface comprising a plurality of solderpads. In step 131 a semiconductor material is provided, thesemiconductor material having a back surface comprising a plurality ofsilver pads. A front surface of the semiconductor material serves as alight-incident surface of the photovoltaic cell. Step 141 involveselectrically coupling, at a plurality of soldering locations, a majorityof the plurality of solder pads on the surface of the expanded metalarticle with the plurality of silver pads on the back surface of thesemiconductor material. The plurality of cuts of the expanded metalarticle is arranged on the photovoltaic cell to relieve stresses inducedby the front metallic article on the front surface of the semiconductormaterial. In step 151, a front metallic article is provided. The frontmetallic article has a plurality of electroformed elementsinterconnected to form a unitary, free-standing piece comprising acontinuous grid. In step 161 the continuous grid of the front metallicarticle is electrically coupled with the front surface of thesemiconductor material.

In some embodiments, the plurality of electroformed elements of themetallic article further comprises a cell-to-cell interconnect that isintegral with the continuous grid, and the method further comprises step171 of coupling the cell-to-cell interconnect to a neighboring backsurface of a neighboring photovoltaic cell. The plurality of cuts of theexpanded metal article is arranged relative to the photovoltaic cell torelieve mechanical stresses induced by the coupling of the metallicarticle to the neighboring photovoltaic cell. That is, the expandedmetal article is positioned on the photovoltaic cell such that the cutshave a specific orientation in relation to other components of thecell—such as the cell-to-cell interconnect and/or to the expansiondirection of the expanded metal article itself. For example, in certainembodiments of step 171, the cell-to-cell interconnect spans across andextends beyond a first edge of the semiconductor material; at least onecut of the plurality of cuts has a length extending in a firstdirection; and the expanded metal article is oriented such that thefirst direction is parallel to the first edge. In some embodiments, theexpanded metal article has an expansion direction in which the pluralityof openings was formed, and at least one cut of the plurality of cutshas a length extending in a first direction that is oriented in theexpansion direction.

The present disclosure further relates to photovoltaic cells produced bythe methods described above. The photovoltaic cell comprises an expandedmetal article electrically coupled to a surface of a semiconductormaterial. The expanded metal article comprises a plurality of firstsegments intersecting a plurality of second segments forming an openingand further comprises a plurality of soldering points, such as solderpads, and the semiconductor material comprises a plurality of points ofcontact for the expanded metal article. The expanded metal article andsemiconductor material can be any of those described above. In oneembodiment, the semiconductor material has a top or light incidentsurface comprising a plurality of silver segments, such as silverfingers, and a majority of the plurality of solder pads on the surfaceof the expanded metal article is in electrical contact with theplurality of silver segments on the semiconductor material. In a secondembodiment, the semiconductor material has a bottom or non-lightincident surface comprising a plurality of silver pads, and a majorityof the plurality of solder pads on the surface of the expanded metalarticle is in electrical contact with the plurality of silver segmentson the semiconductor material.

In certain embodiments of photovoltaic cells of the present disclosure,an expanded metal article comprises a plurality of first segmentsintersecting a plurality of second segments forming a plurality ofopenings. The expanded metal article further comprises a plurality ofcuts, each cut in the plurality of cuts extending across an intersectionof one of the first segments and one of the second segments. Asemiconductor material has a bottom surface comprising a plurality ofsilver pads, where a top surface of the semiconductor material serves asa light-incident surface of the photovoltaic cell. The expanded metalarticle is electrically coupled at a plurality of soldering locations tothe plurality of silver pads on the surface of the semiconductormaterial. A free-standing metallic article is electrically coupled withthe top surface of the semiconductor material to form the photovoltaiccell.

Various combinations and embodiments described above relating to themethods of the present disclosure can also relate to the photovoltaiccells of the present disclosure. The resulting cells can be coupled toform photovoltaic modules.

While the specification has been described in detail with respect tospecific embodiments of the invention, it will be appreciated that thoseskilled in the art, upon attaining an understanding of the foregoing,may readily conceive of alterations to, variations of, and equivalentsto these embodiments. These and other modifications and variations tothe present invention may be practiced by those of ordinary skill in theart, without departing from the scope of the present invention, which ismore particularly set forth in the appended claims. Furthermore, thoseof ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention.

What is claimed is:
 1. A photovoltaic cell comprising: a) an expandedmetal article configured as a mesh, the mesh comprising a plurality offirst segments intersecting a plurality of second segments therebyforming a plurality of openings, wherein the expanded metal article hasa plurality of cuts in the mesh; b) a semiconductor material having afront surface that serves as a light-incident surface of thephotovoltaic cell and a back surface opposite the front surface, whereinthe expanded metal article is electrically coupled to the back surfaceof the semiconductor material; and c) a front metallic articlecomprising a plurality of electroformed elements interconnected to forma unitary, free-standing piece comprising a continuous grid, wherein thecontinuous grid of the front metallic article is electrically coupled tothe front surface of the semiconductor material; wherein: the pluralityof cuts of the expanded metal article is arranged on the photovoltaiccell to relieve stresses induced by the front metallic article on thefront surface of the semiconductor material; the expanded metal articlehas a surface comprising a plurality of solder pads; the back surface ofthe semiconductor material comprises a plurality of silver pads; theplurality of solder pads is electrically coupled to the plurality ofsilver pads at a plurality of soldering locations; and a cut in theplurality of cuts is within a region between neighboring solderinglocations of the plurality of soldering locations.
 2. The photovoltaiccell of claim 1, wherein: the plurality of electroformed elements of thefront metallic article further comprises a cell-to-cell interconnectthat is integral with the continuous grid; the cell-to-cell interconnectis coupled to a neighboring back surface of a neighboring photovoltaiccell; and the stresses are mechanical stresses induced by the couplingof the front metallic article to the neighboring photovoltaic cell. 3.The photovoltaic cell of claim 2, wherein: the cell-to-cell interconnectspans across and extends beyond a first edge of the semiconductormaterial; at least one cut of the plurality of cuts has a lengthextending in a first direction; and the expanded metal article isoriented such that the first direction is parallel to the first edge. 4.The photovoltaic cell of claim 1, wherein: the expanded metal articlehas an expansion direction in which the plurality of openings wasformed; and at least one cut of the plurality of cuts has a lengthextending in a first direction that is oriented in the expansiondirection.
 5. The photovoltaic cell of claim 4, wherein the firstdirection is oriented in a short way of the plurality of openings. 6.The photovoltaic cell of claim 1, wherein each cut in the plurality ofcuts creates a discontinuity in the mesh of the expanded metal article.7. The photovoltaic cell of claim 1, wherein the plurality of cuts isarranged as an array having array dimensions configured to accommodate adifference in coefficient of thermal expansion between the expandedmetal article and the semiconductor material.
 8. The photovoltaic cellof claim 1, wherein the mesh of the expanded metal article spans theback surface of the semiconductor material.
 9. The photovoltaic cell ofclaim 1, wherein each opening in the plurality of openings is diamondshaped, each opening having a width from 3 mm to 7 mm, and a length from10 mm to 15 mm.
 10. The photovoltaic cell of claim 1, wherein each ofthe first segments and each of the second segments have a width from 1mm to 5 mm.
 11. The photovoltaic cell of claim 1, wherein the expandedmetal article has a thickness from 75 microns to 150 microns.
 12. Thephotovoltaic cell of claim 1, wherein the photovoltaic cell has apercent open area greater than 80%.
 13. The photovoltaic cell of claim1, wherein: a first set of cuts in the plurality of cuts is configuredto relieve thermal stresses caused by a difference in coefficient ofthermal expansion between the expanded metal article and thesemiconductor material; and a second set of cuts in the plurality ofcuts is arranged to relieve mechanical stresses induced by coupling acell-to-cell interconnect of the front metallic article to a neighboringback surface of a neighboring photovoltaic cell, the cell-to-cellinterconnect being integral with the continuous grid of the frontmetallic article.